Cognitive Load is a term that refers to the load on working memory during instruction. Working memory (also referred to as Short term memory, depending on the specific theory is a theoretical construct within Cognitive psychology that refers to the This instruction may be aimed at teaching learners problem solving skills, thinking and reasoning skills (including perception, memory, language, etc. Problem solving forms part of thinking. Considered the most complex of all intellectual functions problem solving has been defined as higher-order Cognitive )]
Most would agree that people learn better when they can build on what they already understand (known as a schema), but the more a person has to learn in a shorter amount of time, the more difficult it is to process that information in working memory. A schema (pl schemata) in Psychology and Cognitive science, is a mental structure that represents some aspect of the world Consider the difference between having to study a subject in one's native language versus trying to study a subject in a foreign language. A language is a dynamic set of visual auditory or tactile Symbols of Communication and the elements used to manipulate them The cognitive load is much higher in the second instance because the brain must work to translate the language while simultaneously trying to understand the new information.
Another aspect of cognitive load theory involves understanding how many discrete units of information can be retained in short term memory before information loss occurs. Short-term memory, sometimes referred to as "primary" "working" or "active" Memory, is said to hold a small amount of information for about 20 An example that seems to be commonly cited of this principle is the use of 7-digit phone numbers, based on the theory that most people can only retain seven "chunks" of information in their short term memory. Refer to Chunking (psychology). In Cognitive psychology and Mnemonics, chunking refers to a strategy for making more efficient use of short-term memory by recoding information
"Cognitive load theory has been designed to provide guidelines intended to assist in the presentation of information in a manner that encourages learner activities that optimize intellectual performance" (Sweller, van Merriënboer, and Paas, 1998, p. 251).  Sweller's theory employs aspects of information processing theory to emphasize the inherent limitations of concurrent working memory load on learning during instruction. John Sweller is an Australian educational psychologist who is best known for formulating an influential theory of Cognitive load. Information processing is the change (processing of Information in any manner detectable by an observer. Working memory (also referred to as Short term memory, depending on the specific theory is a theoretical construct within Cognitive psychology that refers to the It makes use of schemas as the unit of analysis for the design of instructional materials. A schema (pl schemata) in Psychology and Cognitive science, is a mental structure that represents some aspect of the world
The history of cognitive load theory can be traced back to the beginning of Cognitive Science and the work of G.A. Miller (1956). George Armitage Miller, born February 3, 1920 in Charleston, West Virginia) is a professor of Psychology at Princeton University Miller was perhaps the first to suggest our working memory capacity was limited in his classic paper . Working memory (also referred to as Short term memory, depending on the specific theory is a theoretical construct within Cognitive psychology that refers to the He suggested we are only able to hold seven plus or minus two digits of information in our short term memories. Miller's early work was built upon by many researchers in the ensuing decades. Perhaps most notably by that of Simon and Chase (1973) who also used the term "chunk" to describe how experts use their short term memories. As novices learn, they begin to see patterns in the world around them.  These patterns can be combined with other patterns. . . this chunking of memory components has also been described as schema construction.
John Sweller developed cognitive load theory while studying problem solving . John Sweller is an Australian educational psychologist who is best known for formulating an influential theory of Cognitive load. While studying learners as they solved problems, he and his associates found that learners often use a problem solving strategy called means-ends analysis. Means-Ends Analysis (MEA is a technique used in Artificial Intelligence for controlling search in Problem solving computer programs He suggests problem solving by means-ends analysis requires a relatively large amount of cognitive processing capacity, which may not be devoted to schema construction. Instead of problem solving, Sweller suggests Instructional designers should limit cognitive load by designing instructional materials like worked-examples, or goal-free problems.
In the 1990s, Cognitive load theory was applied in several contexts and the empirical results from these studies led to the demonstration of several learning effects: the completion-problem effect ; Modality effect ; Split-attention effect ; the Worked-example effect  and the expertise reversal effect . Multimedia learning is the common name used to describe a the “Cognitive theory of Multimedia learning” (Mayer and Moreno 1998 Moreno and Mayer 1999 Mayer 2001 The split-attention effect is a learning effect inherent within some poorly designed instructional materials The worked-example effect is a learning effect predicted by cognitive load theory (Sweller 1988
Cognitive load theory has broad implications for Instructional design (Sweller, 1999). Instructional Design is the practice of creating instructional tools and content to help facilitate learning most effectively This theory provides a general framework for instructional designers for it allows them to control the conditions of learning, within an environment, or more generally within most instructional materials. Specifically, it provides empirically-based guidelines that help instructional designers to decrease extraneous cognitive load during learning, and refocus that learner's attention toward germane materials, increasing germane (schema related) cognitive load. This theory differentiates between three types of cognitive load: intrinsic cognitive load, germane cognitive load, and extraneous cognitive load 
The term "Intrinsic cognitive load" was first described by Chandler and Sweller (1991). Intrinsic cognitive load is the inherent level of difficulty associated with instructional materials Germane cognitive load is that load devoted to the processing construction and automation of schemas Extraneous cognitive load is the working memory load experienced by learners as they interact with instructional materials  Accordingly all instruction has an inherent difficulty associated with it (e. g. , the calculation of 2 + 2, versus solving a differential equation ). A differential equation is a mathematical Equation for an unknown function of one or several variables that relates the values of the This inherent difficulty may not be altered by an instructor. However many schemas may be broken into individual "subschemas" and taught in isolation, to be later brought back together and described as a combined whole .
Extraneous cognitive load is generated by the manner in which information is presented to learners and is under the control of instructional designers (Pollock, Chandler & Sweller, 2002). This load can be attributed to the design of the instructional materials.
Sweller provides a wonderful example of extraneous cognitive load in his 2006 book, when he describes two possible ways to describe a square to a student . A square is a visual and should be described using a visual medium. Certainly an instructor can describe a square in a verbal medium, but it takes just a second and far less effort to see what the instructor is talking about when a learner is shown a square, rather than having one described verbally. In this instance, the efficiency of the visual medium is preferred. This is because it does not unduly load the learner with unnecessary information. This unnecessary cognitive load is described as extraneous cognitive load.
Germane load was first described by Sweller, van Merrienboer and Paas in 1998.  It is that load devoted to the processing, construction and automation of schemata. A schema (pl schemata) in Psychology and Cognitive science, is a mental structure that represents some aspect of the world While intrinsic load is generally thought to be immutable, instructional designers can manipulate extraneous and germane load. It is suggested that they limit extraneous load and promote germane load .
Paas and van Merriënboer (1993) developed a construct (known as relative condition efficiency) which helps researchers measure perceived mental effort, an index of cognitive load. This construct provides a relatively simple means of comparing instructional conditions. It combines mental effort ratings with performance scores. Group mean z-scores are graphed and may be compared with a one-way ANOVA.
Paas and van Merriënboer (1993) used relative condition efficiency to compare three instructional condition (worked examples, completion problems, and discovery practice). They found learners who studied worked examples were the most efficient, followed by those who used the problem completion strategy. Since this early study many other researchers have used this and other constructs to measure cognitive load as it relates to learning and instruction (Paas, Tuovinen, Tabbers, & Van Gerven, 2003).
Scandura (1971) and Voorhies & Scandura (1977) found evidence that individuals systematically differ in their processing capacity.   A series of experiments support the assumption that each individual has a fixed capacity for processing information, irrespective of the task in question, or more accurately, irrespective of the processes an individual uses in solving any given task. Tasks ranged from remembering simple lists, lists supplemented with a fixed constant and simple arithmetic.
Identifying the processing capacity of individuals could be extremely useful in further adapting instruction (or predicating the behavior) of individuals. Accordingly, further research would clearly be desirable. It should be cautioned that this type of research is very demanding. First, it is essential to compute the memory load imposed by detailed analysis of the processes to be used. Second, it is essential to insure that individual subjects are actually using those processes. The latter requires intensive pre-training.
The ergonomic approach seeks a quantitative neurophysiological expression of cognitive load which can be measured using common instruments. Fredericks T. K. , Choi S. D,. Hart J. , Butt S. E. , and Mital A. (2005), for example, used the heart rate-blood pressure product (RPP) as a measure of both cognitive and physical occupational workload. Measuring heart rate The Pulse rate (which in most people is identical to the heart rate can be measured at any point on the body where an Artery 's pulsation Blood pressure is also the title of a short story by Damon Runyan in Guys and Dolls and Other Stories  They believe that it may be possible to use RPP measures to set limits on workloads and for establishing work allowance.
For Ergonomics Standards See
ISO 10075-1:2000 Ergonomic Principles Related to Mental Work-load - Part 1: General Terms and Definitions
ISO 10075-2:2000 Ergonomic Principles Related To Mental Workload - Part 2 - Design Principles
ISO 10075-3:2004 Ergonomic Principles Related To Mental Workload - Part 3: Principles And Requirements Concerning Methods For Measuring And Assessing Mental Workload